[vikky@server v3tv]$ cat hello.c 
/* Kernel Programming */
#define MODULE
#define LINUX
#define __KERNEL__

#include <linux/module.h>  /* Needed by all modules */
#include <linux/kernel.h>  /* Needed for KERN_ALERT */


int init_module(void)
{
        printk("<1>Hello world 1.\n");

        // A non 0 return means init_module failed; module can't be loaded.
        return 0;
}

void cleanup_module(void)
{
        printk(KERN_ALERT "Goodbye world 1.\n");
}  

MODULE_LICENSE("GPL");
[vikky@server v3tv]$ cat tmp.mak 
TARGET  := hello
WARN    := -W -Wall -Wstrict-prototypes -Wmissing-prototypes
INCLUDE := -isystem /lib/modules/`uname -r`/build/include
CFLAGS  := -O2 -DMODULE -D__KERNEL__ ${WARN} ${INCLUDE}
CC      := gcc

${TARGET}.o: ${TARGET}.c

.PHONY: clean

clean:
        rm -rf ${TARGET}.o
[vikky@server v3tv]$ make -f tmp.mak 
gcc -O2 -DMODULE -D__KERNEL__ -W -Wall -Wstrict-prototypes -Wmissing-prototypes -isystem /lib/modules/`uname -r`/build/include   -c -o hello.o hello.c
hello.c:2:1: warning: "MODULE" redefined
<command line>:1:1: warning: this is the location of the previous definition
hello.c:4:1: warning: "__KERNEL__" redefined
<command line>:1:1: warning: this is the location of the previous definition
In file included from /lib/modules/2.6.21.5/build/include/linux/prefetch.h:14,
                 from /lib/modules/2.6.21.5/build/include/linux/list.h:8,
                 from /lib/modules/2.6.21.5/build/include/linux/module.h:10,
                 from hello.c:6:
/lib/modules/2.6.21.5/build/include/asm/processor.h:77: error: ‘CONFIG_X86_L1_CACHE_SHIFT’ undeclared here (not in a function)
/lib/modules/2.6.21.5/build/include/asm/processor.h:77: error: requested alignment is not a constant
/lib/modules/2.6.21.5/build/include/asm/processor.h:233: error: requested alignment is not a constant
In file included from /lib/modules/2.6.21.5/build/include/linux/kobject.h:25,
                 from /lib/modules/2.6.21.5/build/include/linux/module.h:17,
                 from hello.c:6:
/lib/modules/2.6.21.5/build/include/linux/rwsem.h:24:65: error: asm/rwsem.h: No such file or directory
In file included from /lib/modules/2.6.21.5/build/include/linux/module.h:17,
                 from hello.c:6:
/lib/modules/2.6.21.5/build/include/linux/kobject.h:178: error: field ‘rwsem’ has incomplete type
In file included from /lib/modules/2.6.21.5/build/include/linux/memory_hotplug.h:7,
                 from /lib/modules/2.6.21.5/build/include/linux/mmzone.h:463,
                 from /lib/modules/2.6.21.5/build/include/linux/gfp.h:4,
                 from /lib/modules/2.6.21.5/build/include/linux/slab.h:14,
                 from /lib/modules/2.6.21.5/build/include/linux/percpu.h:5,
                 from /lib/modules/2.6.21.5/build/include/asm/local.h:4,
                 from /lib/modules/2.6.21.5/build/include/linux/module.h:19,
                 from hello.c:6:
/lib/modules/2.6.21.5/build/include/linux/notifier.h:62: error: field ‘rwsem’ has incomplete type
make: *** [hello.o] Error 1
[vikky@server v3tv]$